Thinking of building an ADU in Costa Mesa? | Check Your Address | The ADU Guide (2024)

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Everything there is to know about building an Additional Dwelling Unit inCosta Mesa, CA

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What is an ADU?

Most cities and planning authorities, as in Costa Mesa, define accessory dwelling units (ADUs) as small housing units situated on the same lot as a principal residence which can either be attached to or detached from the primary home structure. Around California, ADUs are under other, more popular pseudonyms, such as granny flats or mother-in-law suites. Some homeowners will rent their ADUs out to generate additional income. Though an ADU can still be a worthwhile investment, even if you don’t plan on renting it out, building a dwelling unit will increase the value of your property and provide more space and privacy for friends and family.

Thinking of building an ADU in Costa Mesa? | Check Your Address | The ADU Guide (1)

Getting Started on

Steps for getting started on your ADU Project:

While “accessory:” might make an ADU sound minor, in practice, building such a unit is like building a tiny house and is, by no means, an easy undertaking. To help you wrap your mind around what to expect and brainstorm how to get things going, here are a few quick pointers:

  • Is the unit intended for rent? For family members?
  • Run a Property Check – click here for ADU’s FREE Property Check.
  • Contact the Orange County municipal zoning office and ask about the regulations and obstacles of your project.
  • Hire a professional to help you sketch out several rough design ideas.
  • Seek out local general contractors familiar with your area and its regulations.
  • Together with your contractor, draft permit-ready sketches for purposes of zoning and construction.
  • Pay the necessary permit fees and submit plans to pass building code criteria.
  • Once the permits are issued, begin construction.

ADU Ordinance and Opportunity in Costa Mesa

Across Costa Mesa and its population of 113003 residents, more and more people are finding it hard to find suitable homes that fit their budgets. As a result, the local government has taken measures to increase the availability of lower-priced homes – mainly by instituting legislation to regulate the housing market. Recently, there has been growing attraction to Accessory Dwelling Units, or ADUs. California planning authorities modified ADU building regulations, allowing homeowners to construct a separate unit on their property with living spaces for family members or rental tenants. These amendments to the laws enable more people to build ADUs within their homes and open up opportunities for more people to live affordably. This legislation provides homeowners with incredible opportunities and the potential to grow their monthly income through rent.

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ADU Zoning and Legal Considerations in Costa Mesa

According to California state law, any single-family home is allowed to build an Accessory Dwelling Unit. If the owner is living in the house, they may also construct a junior unit (independent living structure, no more than 500 square feet, within the walls of a single-family residence).
In some areas, a local health officer may require to approve private sewage disposal in your dwelling unit.
According to AB 671, Housing elements must include a plan which incentivizes and promotes the construction of affordable-to-rent dwelling units. The California Department of Housing and Community Development must provide a list of state grants and financial incentives to plan, construct and operate affordable tiny homes. (Gov. Code, § 65583; Health & Safety Code, § 50504.5).
This same ordinance seeks to ease requirements such as parking, size, and fees so that they’re “not so arbitrary, excessive or burdensome to unreasonably restrict the ability of homeowners to create accessory dwelling units” in areas where tiny home construction is allowed.

Thinking of building an ADU in Costa Mesa? | Check Your Address | The ADU Guide (2)

Zoning Requirements for Types of ADUs

A Detached ADU, sometimes called a backyard ADU, is entirely separate from the main home, sharing no walls. These typically are allowed to be between 500-1,200 square feet, depending on the number of rooms. The Attached ADU is very similar, except that it shares a wall with the main living structure. Junior Accessory Dwelling Units (JADUs) must be built from an existing home part and cannot exceed 500 sqft. The minimum legal size for these is 150 sqft.

Scroll down for more information about the different types of ADUs and see which is the best fit for your property!

Parking Requirements for ADUs

Certain ADUs are exempt from parking requirements. According to Government Code section 65852.2, subdivisions (d)(1-5) and (j)(10), “local agency shall not impose ADU parking standards” on the following types of ADUs:

  • Accessory Dwelling Units within half a mile of walking distance of any public transit.
  • ADUs within a historic district.
  • Dwelling units that are “part of the proposed or existing primary residence or an accessory structure.”
  • When on-street parking permits are required.

Why Build an ADU Now?

In accordance with Government Code section 65852.150, the California Legislature declared that California is facing a severe housing crisis; it further stated that ADUs are a necessary innovation in meeting low-cost housing requirements for family members, students, the elderly, in-home health care providers, people with disabilities, and others. Therefore, Additional Dwelling Units are essential to the CA housing supply.

ADU Impact Fee Exemptions

If an ADU is less than 750 square feet, it is exempt from impact fees from local agencies, special districts, and water corporations. If it meets or exceeds this size limit, impact fees “shall be charged proportionately with the square footage of the ADU to the square footage of the primary dwelling unit.” In such a case, the impact fee should always be at most that of the primary dwelling.
* School districts may (if they so choose) levy impact fees for ADUs larger than 500 square feet as per Section 17620 of the Education Code. ADUs smaller than 500 square feet are exempt from school impact fees.

Financing an ADU

Have you decided to pursue an Additional Dwelling Unit but aren’t sure how to finance it? There are many options, from well-known home equity or renovation loans to lesser-known alternatives such as cash-out refinancing your mortgage, a PACE loan, and government ADU programs. Keep in mind that as a homeowner, you may be eligible for loans against the value of your home, although it may create certain significant risks. We recommend speaking with one of our specialists regarding the best way to finance your ADU in Costa Mesa, CA.

Government ADU Grant Programs

According to the California Department of Housing and Community, the CalHFA ADU Grant Program provides up to $40,000 in assistance to reimburse homeowners for predevelopment and non-recurring closing costs necessary to build and occupy an Accessory Dwelling Unit. Predevelopment costs include site prep, architectural designs, permits, soil tests, impact fees, property surveys, and energy reports. To learn more about different ADU grant programs, please visit our Government ADU Grant Programs page.

Thinking of building an ADU in Costa Mesa? | Check Your Address | The ADU Guide (3)

Types of ADU

Thinking of building an ADU in Costa Mesa? | Check Your Address | The ADU Guide (4)

Attached ADU

A small apartment unit built as an add-on to your home, sharing at least one wall with the primary building. An attached unit usually connects to the primary structure’s water and power lines, but it provides for all independent living needs. The best thing about a detached ADU is its separate entrance. As such, if you live on a property in Costa Mesa with limited available space, an attached ADU could be a great solution.

Thinking of building an ADU in Costa Mesa? | Check Your Address | The ADU Guide (5)

Detached ADU

A detached ADU is an independent structure that stands and functions as its own house, albeit smaller than the primary home. It includes all the necessary amenities for its inhabitants. Most ADU laws, as is the case in Costa Mesa California, stipulate that if you wish to build a detached ADU, you need to set aside an area of your property and create good boundaries to provide the unit’s residents with privacy. Large detached ADUs can often earn high rental rates because they offer renters more flexibility.

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Garage Conversion

Garage conversions are trendy ideas for maximizing your property's earning potential. As the name suggests, a garage conversion is simply a remake of what already exists - namely, an attached or detached garage. Converting your garage area can give you much-needed living space or gain you regular extra income!

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Above Garage ADU​

An Above Garage-Attached Dwelling Unit (ADU) provides an affordable option for homeowners looking to rent out their space while still being able to use their garage. By installing an ADU on top of your current garage, you'll have plenty of extra room for tenants without giving up the much-needed parking and storage space.

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Interior Conversion

A converted space inside your house, letting you create your own tiny home within a home. Interior ADUs are, as with all ADUs, meant to be independent living quarters. Therefore, these spaces require plumbing and ventilation for the unit's separate kitchen and bath, and they will most likely share utility services and mechanical appliances with the central unit. Currently, in Costa Mesa, CA, these units are the most common form of ADU homes as they're easy to maintain and affordable. So don't hesitate to think about building one!

Thinking of building an ADU in Costa Mesa? | Check Your Address | The ADU Guide (9)

Junior ADU (JADU)​

A Junior Accessory Dwelling Unit (JADU) is the Single Family ADU’s (the standard ADU) little sibling but has different restrictions to help keep costs down while ensuring that they provide adequate living facilities. For example, a JADU can only be built as part of a single-family home, existing or proposed single-family home, or within an accessory structure, such as a detached garage or carport. A JADU shares utilities and mechanical appliances with the main house.

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The Guide to Building an Accessory Dwelling Unit in Costa Mesa, CA.

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Thinking of building an ADU in Costa Mesa? | Check Your Address | The ADU Guide (2024)

FAQs

Can you build ADU in Costa Mesa? ›

If you have a single-family home, you can for the most part have one or two ADUs on it. The number of ADUs allowed on multi-family properties depends on the type of ADU constructed and how many dwelling units are already on the property.

How much does an ADU cost in Orange County CA? ›

Total cost to build an ADU in Orange County

A detached accessory dwelling unit with one level typically costs between $200,000 and $400,000. The main factors that dictate the cost of your project will be site conditions, the size of the structure, and of course, the finishes you choose inside and out.

What size bathroom is needed for an ADU? ›

An ADU living room and bedroom can be at least 70 square feet, and the kitchen must measure at least 50 square feet. The bathroom must measure at least 30 square feet and have a sink, shower or tub, and toilet available. What Extra Features Can You Add to an Accessory Dwelling Unit California?

What is the size limit for an ADU in Orange County? ›

ADU's may be attached or detached to the primary dwelling unit. dwelling unit or ADU. Accessory Dwelling Units: Size: Attached ADU: Up to 50% of the area of the primary dwelling unit, to a maximum of 1,200 square feet; 800 square foot maximum within the setback area where permitted.

How far can an ADU be from the main house? ›

All in all the maximum size for a granny flat is 1,200 sq. ft. or half the size of the existing residence. A detached ADU must be ten feet away from the main residence and five feet away from any property lines.

Can I build an ADU in my front yard California? ›

A local agency may still apply front yard setbacks for ADUs, but front yard setbacks cannot preclude an ADU of at least 800 square feet and must not unduly constrain the creation of all types of ADUs. (Gov. Code, § 65852.2, subd.

What is the cheapest way to build an ADU in California? ›

What is the cheapest way to build an ADU? Typically, the most cost-effective ADU type is a garage conversion ADU (if your garage is in sound condition and requires no major fixes). Your ADU can use the existing structure and cut down on construction costs, which take up a significant portion of your total cost.

How much is a 2 bedroom ADU in California? ›

TABLE: Cost To Build an ADU in San Diego, California
TypeSizeTypical All-In Cost
1BR/1BA500 sqft$300K
2BR/1BA750 sqft$350K
2BR/2BA1000 sqft$425K
3BR/2BA1200 sqft$450K+

How much does it cost to build a 1000 sq ft ADU in California? ›

An ADU in California costs approximately $125 to $300 per square foot, but some can reach as high as $600 per square foot. Your costs will vary depending on unit size, location, lot conditions, building and safety regulations, zoning requirements, and personal preferences like fit and finish.

What is an ADU without a kitchen called? ›

Often called a granny flat or backyard cottage, ADUs are either an attached or detached self-contained unit that has a kitchen, bathroom, and sleeping areas. If the unit doesn't have a kitchen or bathroom it's not considered habitable and not an ADU — without these spaces you have a shed.

How many bedrooms can an ADU have in California? ›

California state law does not allow a limit on the number of bedrooms in an ADU. Limiting the number of bedrooms can be considered discriminatory towards protected classes and impede the development of new ADUs. Local governments cannot adopt ordinances that impose bedroom limits for new ADUs.

What is a good size ADU? ›

However, California prohibits such untraditional houses from exceeding certain size limits. According to California state laws, an ADU should have a floor area of up to 800 square feet, a 16-foot ceiling height, and a 4-feet setback distance.

Can an ADU be larger than the primary residence? ›

For attached ADUs, the square footage can never be more than 50% that of the main residence. For detached ADUs, if the planned size exceeds that of the primary dwelling, the ADU size is limited to a maximum of 800 square feet. This is one example of the complexity of the laws around how big an ADU can be in California.

Can you have a 2 story ADU in California? ›

Detached ADUs may be built up to two stories not exceeding 20 feet in height. Conversion of an existing accessory structure or a portion of the existing primary residence to an ADU is not subject to height requirements.

What is the largest that a detached ADU could be? ›

ADU Size Limits

Detached ADUs can be up to 1200 sq ft. Detached ADUs with one bedroom or less can be 800 sq ft. Detached ADUs with two or more bedrooms can be up to 1000 sq ft.

How much is a permit to build an ADU in California? ›

Before you can start building your ADU, you will need permission from your local planning department. These permissions are called permits, and their costs vary depending on your location. Building permits range from $2,000 to $10,000, whereas city fees can range from $3,000 to $11,000.

Where can I build an ADU in California? ›

Assembly Bill 68 allows landlords and homeowners to add 2 more units – an ADU and a Junior Accessory Dwelling Unit (JADU) – on any residential lot. This means you can legally create a triplex on every single lot (if your lot meets size and setback requirements) according to the 2024 ADU laws in California.

How big can an ADU be in Contra Costa County? ›

ADUs in Contra Costa can be no larger than 1,200 square feet and 16 feet tall. An ADU must have its own kitchen and bathroom and function as a complete, independent dwelling separate to the main residence on the lot.

Can you build an ADU on a rental property in California? ›

Yes, you can rent your ADU. And you can build an accessory unit on a rental property for ADU rental income. Previously, California state law enforced specific legislation regarding owner occupancy requirements.

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